More Like this

1. Calibration and Uncertainty Quantification for Single-Ended Raman-Based Distributed Temperature Sensing: Case Study in a 800 m Deep Coaxial Borehole Heat Exchanger

   https://doi.org/10.3390/s23125498  

   Mazzotti Pallard, Willem Mazzotti; Lazzarotto, Alberto; Acuña, José; Palm, Björn (June 2023, Sensors)

   Raman-based distributed temperature sensing (DTS) is a valuable tool for field testing and validating heat transfer models in borehole heat exchanger (BHE) and ground source heat pump (GSHP) applications. However, temperature uncertainty is rarely reported in the literature. In this paper, a new calibration method was proposed for single-ended DTS configurations, along with a method to remove fictitious temperature drifts due to ambient air variations. The methods were implemented for a distributed thermal response test (DTRT) case study in an 800 m deep coaxial BHE. The results show that the calibration method and temperature drift correction are robust and give adequate results, with a temperature uncertainty increasing non-linearly from about 0.4 K near the surface to about 1.7 K at 800 m. The temperature uncertainty is dominated by the uncertainty in the calibrated parameters for depths larger than 200 m. The paper also offers insights into thermal features observed during the DTRT, including a heat flux inversion along the borehole depth and the slow temperature homogenization under circulation. 

   more » « less
2. Combining passive and active distributed temperature sensing measurements to locate and quantify groundwater discharge variability into a headwater stream

   https://doi.org/10.5194/hess-26-1459-2022  

   Simon, Nataline; Bour, Olivier; Faucheux, Mikaël; Lavenant, Nicolas; Le Lay, Hugo; Fovet, Ophélie; Thomas, Zahra; Longuevergne, Laurent (January 2022, Hydrology and Earth System Sciences)

   Abstract. Exchanges between groundwater and surface water play a key role for ecosystem preservation, especially in headwater catchments where groundwater discharge into streams highly contributes to streamflow generation and maintenance. Despite several decades of research, investigating the spatial variability in groundwater discharge into streams still remains challenging mainly because groundwater/surface water interactions are controlled by multi-scale processes. In this context, we evaluated the potential of using FO-DTS (fibre optic distributed temperature sensing) technology to locate and quantify groundwater discharge at a high resolution. To do so, we propose to combine, for the first time, long-term passive DTS measurements and active DTS measurements by deploying FO cables in the streambed sediments of a first- and second-order stream in gaining conditions. The passive DTS experiment provided 8 months of monitoring of streambed temperature fluctuations along more than 530 m of cable, while the active DTS experiment, performed during a few days, allowed a detailed andaccurate investigation of groundwater discharge variability over a 60 m length heated section. Long-term passive DTS measurements turn out to bean efficient method to detect and locate groundwater discharge along several hundreds of metres. The continuous 8 months of monitoring allowed the highlighting of changes in the groundwater discharge dynamic in response to the hydrological dynamic of the headwater catchment. However, the quantification of fluxes with this approach remains limited given the high uncertainties on estimates, due to uncertainties on thermal properties and boundary conditions. On the contrary, active DTS measurements, which have seldom been performed in streambed sediments and never applied to quantify water fluxes, allow for the estimation of the spatial distribution of both thermal conductivities and the groundwater fluxes at high resolution all along the 60 m heated section of the FO cable. The method allows for the description of the variability in streambed properties at an unprecedented scale and reveals the variability in groundwater inflows at small scales. In the end, this study shows the potential and the interest of the complementary use of passive and active DTS experiments to quantify groundwater discharge at different spatial and temporal scales. Thus, results show that groundwater discharges are mainly concentrated in the upstream part of the watershed, where steepest slopes are observed, confirming the importance of the topography in the stream generation in headwater catchments. However, through the high spatial resolution of measurements, it was also possible to highlight the presence of local and highly contributive groundwater inflows, probably driven by local heterogeneities. The possibility to quantify groundwater discharge at a high spatial resolution through active DTS offers promising perspectives for the characterization of distributed responses times but also for studying biogeochemical hotspots and hot moments. 

   more » « less
3. Oxygen optodes on oceanographic moorings: recommendations for deployment and in situ calibration

   https://doi.org/10.3389/fmars.2024.1441976  

   Miller, Una Kim; Fogaren, Kristen E; Atamanchuk, Dariia; Johnson, Clare; Koelling, Jannes; Le_Bras, Isabela; Lindeman, Margaret; Nagao, Hiroki; Nicholson, David P; Palevsky, Hilary; et al (November 2024, Frontiers in Marine Science)

   Increasing interest in the deployment of optical oxygen sensors, or optodes, on oceanographic moorings reflects the value of dissolved oxygen (DO) measurements in studies of physical and biogeochemical processes. Optodes are well-suited for moored applications but require careful, multi-step calibrations in the field to ensure data accuracy. Without a standardized set of protocols, this can be an obstacle for science teams lacking expertise in optode data processing and calibration. Here, we provide a set of recommendations for the deployment andin situcalibration of data from moored optodes, developed from our experience working with a set of 60 optodes deployed as part of the Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP). In particular, we detail the correction of drift in moored optodes, which occurs in two forms: (i) an irreversible, time-dependent drift that occurs during both optode storage and deployment and (ii) a reversible and pressure-and-time-dependent drift that is detectable in some optodes deployed at depths greater than 1,000 m. The latter is virtually unidentified in the literature yet appears to cause a low-bias in measured DO on the order of 1 to 3µmol kg⁻¹per 1,000 m of depth, appearing as an exponential decay over the first days to months of deployment. Comparisons of our calibrated DO time series against serendipitous mid-deployment conductivity-temperature-depth (CTD)-DO profiles, as well as biogeochemical (BGC)-ARGO float profiles, suggest the protocols described here yield an accuracy in optode-DO of ∼1%, or approximately 2.5 to 3µmol kg⁻¹. We intend this paper to serve as both documentation of the current best practices in the deployment of moored optodes as well as a guide for science teams seeking to collect high-quality moored oxygen data, regardless of expertise. 

   more » « less
4. Summit Greenland Temperature Logs

   https://doi.org/10.4211/hs.ef0450cbcc394ff598da908b739ed461  

   OSU-UNR, CTEMPs (April 2025, HydroShare)

   This dataset presents physical parameters (temperature, Stokes and anti-Stokes Raman scattering signals) measured during the emplacement of bare single-mode optical fiber within the Greenland Ice Sheet using the Ice Diver melt probe at Summit Station, Greenland (specifically, at 72.5817 N, 38.4578 W). In addition to Stokes and Anti-Stokes signals, the dataset includes englacial temperature profiles derived via Raman distributed temperature sensing (DTS) at 1 m resolution, from ice depths -50 – 355 m (with 0 m representing the top of the borehole). The Raman backscatter signals (Stokes and Anti-Stokes) were captured by the ULTIMA Single Mode Distributed Temperature System (Silixa Ultima Single Mode interrogator) operating at a source wavelength of 1550 nm. Temperature data represent the first 108 hours of cooling (from June 7 – June 12, 2024) following melt probe entrapment in the ice at a depth of ~350 m. Temperature data were calibrated using a section of 25 m of the unreinforced fiber placed in an insulated controlled temperature bath during deployment. Two external PT-100 temperature probes were placed within the bath above and below the spool of fiber optic cable to monitor calibration bath temperatures. External temperature probes were an average of 1.5±0.2 °C warmer than the fiber optic cable. Data records are contained in three Excel spreadsheets (ice_diver_temperatures, Stokes_ice_diver and Anti_Stokes_ice_diver). The first column represents depth below the ice surface, with time in both standard and Matlab datenum format across the top of the spreadsheet. For additional information contact: Scott Tyler styler@unr.edu; Dale Weinbrenner dpw@apl.washington.edu; Sophie Wensman Sophia.Wensman@dri.edu 

   more » « less
5. Laboratory and field evaluation of a low-cost methane sensor and key environmental factors for sensor calibration

   https://doi.org/10.1039/d2ea00100d  

   Lin, Joyce J.; Buehler, Colby; Datta, Abhirup; Gentner, Drew R.; Koehler, Kirsten; Zamora, Misti Levy (April 2023, Environmental Science: Atmospheres)

   Low-cost sensors enable finer-scale spatiotemporal measurements within the existing methane (CH 4 ) monitoring infrastructure and could help cities mitigate CH 4 emissions to meet their climate goals. While initial studies of low-cost CH 4 sensors have shown potential for effective CH 4 measurement at ambient concentrations, sensor deployment remains limited due to questions about interferences and calibration across environments and seasons. This study evaluates sensor performance across seasons with specific attention paid to the sensor's understudied carbon monoxide (CO) interferences and environmental dependencies through long-term ambient co-location in an urban environment. The sensor was first evaluated in a laboratory using chamber calibration and co-location experiments, and then in the field through two 8 week co-locations with a reference CH 4 instrument. In the laboratory, the sensor was sensitive to CH 4 concentrations below ambient background concentrations. Different sensor units responded similarly to changing CH 4 , CO, temperature, and humidity conditions but required individual calibrations to account for differences in sensor response factors. When deployed in-field, co-located with a reference instrument near Baltimore, MD, the sensor captured diurnal trends in hourly CH 4 concentration after corrections for temperature, absolute humidity, CO concentration, and hour of day. Variable performance was observed across seasons with the sensor performing well ( R 2 = 0.65; percent bias 3.12%; RMSE 0.10 ppm) in the winter validation period and less accurately ( R 2 = 0.12; percent bias 3.01%; RMSE 0.08 ppm) in the summer validation period where there was less dynamic range in CH 4 concentrations. The results highlight the utility of sensor deployment in more variable ambient CH 4 conditions and demonstrate the importance of accounting for temperature and humidity dependencies as well as co-located CO concentrations with low-cost CH 4 measurements. We show this can be addressed via Multiple Linear Regression (MLR) models accounting for key covariates to enable urban measurements in areas with CH 4 enhancement. Together with individualized calibration prior to deployment, the sensor shows promise for use in low-cost sensor networks and represents a valuable supplement to existing monitoring strategies to identify CH 4 hotspots. 

   more » « less